The present invention relates to an RF coil (radio frequency coil) and a magnetic resonance imaging apparatus, and particularly to an RF coil having disable circuits which preclude the RF coil from coupling with other coils and a magnetic resonance imaging apparatus using this RF coil.
The magnetic resonance imaging (MRI) apparatus operates to apply a gradient magnetic field and an RF magnetic field to a subject of imaging which is placed in the internal space of a magnet system, i.e., the space where a static magnetic field is formed, so that a magnetic resonance signal is generated in the subject, and form (recompose) a tomographic image based on a received magnetic resonance signal.
An RF coil is used for the application of RF magnetic field and the reception of magnetic resonance signal. In case the application of RF magnetic field and reception of magnetic resonance signal are implemented with separate RF coils, disable circuits which preclude the coupling of these coils are provided for each of the sending coil and receiving coil.
Each disable circuit is formed as a parallel connection of a capacitor and a serial circuit of an inductor and a diode.
A d.c. forward bias signal is used to turn on the diodes thereby to form LC circuits, and their high-impedance state caused by the parallel resonation is utilized to disable the RF coil, thereby performing the decoupling. A d.c. reverse bias signal is used to turn off the diodes thereby to dissolve the parallel connection of the capacitor and diode and enable the RF coil, thereby allowing the transmission or reception of the RF signal. The receiving coil is disabled when the RF signal is transmitted, and the sending coil is disabled when the magnetic resonance signal is received.
Supplying the d.c. bias signal from the feed point of the RF signal by the common use of the RF signal feed line is advantageous in reducing signal lines, however, the d.c. bias current flowing through the main loop of the RF coil and thus forming a d.c. magnetic field will deteriorate the accuracy of the static magnetic field.
An object of the present invention is the accomplishment of an RF coil which does not suffer the adverse influence of the bias current of the disable circuits on the static magnetic field, and a magnetic resonance imaging apparatus using this RF coil.
(1) The invention at a first viewpoint intending to solve the above-mentioned problem resides in an RF coil having disable circuits, each of which is a parallel connection of a capacitor and a serial circuit of an inductor and a diode and is connected in series to the coil loop, and being characterized by including RF choke circuits which form a d.c. bias feed path for the diodes by connecting points of equal RF potential on the coil loop.
The invention at this viewpoint is designed to arrange a bias feed circuit of the disable circuit based on the connection of points of equal RF potential on the coil loop through RF choke circuits. Accordingly, the d.c. bias current flows through the RF choke circuits instead of the main loop of the RF coil, while the RF signal goes through the main loop instead of the RF choke circuits, and consequently it is possible to feed the d.c. bias current and RF signal at the same point.
(2) The invention at other viewpoint intending to solve the above-mentioned problem resides in an RF coil of the item (1) , which is characterized by including a plurality of linear main current paths lying in parallel to each other on a plane, and roundabout current paths which lie round beside the main current paths on the plane to connect the main current paths in series so that the main current paths have a same current direction, and having the disable circuits lying on the roundabout current paths.
The invention at this viewpoint is designed to dispose the disable circuits on the roundabout current paths of the coil loop, and consequently a magnetic field created by the d.c. bias current does not affect the static magnetic field of the imaging space.
(3) The invention at other viewpoint intending to solve the above-mentioned problem resides in an RF coil of the item (1), which is characterized by including first current paths which include a plurality of linear current paths lying in parallel to each other on a plane, second current paths which include a plurality of linear current paths lying in parallel to each other, and lie on the plane to have a parallel mirror-image relation with the first current paths, and third current paths which lie round beside the first and second current paths along the plane to connect all linear current paths of the first and second current paths in series so that the linear current paths have a same current direction, and having the disables circuits lying on the third current paths.
The invention at this viewpoint is designed to dispose the disable circuits on the third current paths, i.e., the roundabout current paths, of the coil loop, and consequently a magnetic field created by the d.c. bias current does not affect the static magnetic field of the imaging space.
(4) The invention at other viewpoint intending to solve the above-mentioned problem resides in an RF coil of the item (1), which is characterized by including first current paths which include a plurality of linear current paths lying in parallel to each other on a first plane, second current paths which include a plurality of linear current paths lying in parallel to each other, and lie on the first plane to have a parallel mirror-image relation with the first current paths, third current paths which lie round beside the first and second current paths along the first plane to connect all linear current paths of the first and second current paths in series so that the linear current paths have a same current direction, fourth current paths which include a plurality of linear current paths lying in parallel to the current path direction of the first current paths on a second plane which confronts the first plane in parallel by being spaced out therefrom, fifth current paths which include a plurality of linear current paths lying in parallel to each other, and lie on the second plane to have a parallel mirror-image relation with the fourth current paths, and sixth current paths which lie round beside the fourth and fifth current paths along the second plane to connect all linear current paths of the fourth and fifth current paths in series so that the linear current paths have the same current direction, and having the disable circuits lying on the third and sixth current paths.
The invention at this viewpoint is designed to dispose the disable circuits on the third and sixth current paths, i.e., the roundabout current paths, of the coil loop, and consequently a magnetic field created by the d.c. bias current does not affect the static magnetic field of the imaging space.
(5) The invention at other viewpoint intending to solve the above-mentioned problem resides in an RF coil of the item (1), which is characterized by including first current paths which include a plurality of linear current paths lying in parallel to each other on a first plane, second current paths which include a plurality of linear current paths lying in parallel to each other, and lie on the first plane to have a parallel mirror-image relation with the first current paths, third current paths which lie round beside the first and second current paths along the first plane to connect all linear current paths of the first and second current paths in series so that the linear current paths have a same current direction, seventh current paths which include a plurality of linear current paths lying in parallel to each other along the direction perpendicular to the current path direction of the first current paths on a third plane which confronts the first plane in parallel and in close vicinity thereto, eighth current paths which include a plurality of linear current paths lying in parallel to each other, and lie on the third plane to have a parallel mirror-image relation with the seventh current paths, and ninth current paths which lie round beside the seventh and eighth current paths along the third plane to connect all linear current paths of the seventh and eighth current paths in series so that the linear current paths have a same current direction, and having the disable circuits lying on the third and ninth current paths.
The invention at this viewpoint is designed to dispose the disable circuits on the third and ninth current paths, i.e., the roundabout current paths, of the coil loop, and consequently a magnetic field created by the d.c. bias current does not affect the static magnetic field of the imaging space.
(6) The invention at other viewpoint intending to solve the above-mentioned problem resides in an RF coil of the item (1), which is characterized by including first current paths which include a plurality of linear current paths lying in parallel to each other on a first plane, second current paths which include a plurality of linear current paths lying in parallel to each other, and lie on the first plane to have a parallel mirror-image relation with the first current paths, third current paths which lie round beside the first and second current paths along the first plane to connect all linear current paths of the first and second current paths in series so that the linear current paths have a same current direction, seventh current paths which include a plurality of linear current paths lying in parallel to each other along the direction perpendicular to the current path direction of the first current paths on a third plane which confronts the first plane in parallel and in close vicinity thereto, eighth current paths which include a plurality of linear current paths lying in parallel to each other, and lie on the third plane to have a parallel mirror-image relation with the seventh current paths, ninth current paths which lie round beside the seventh and eighth current paths along the third plane to connect all linear current paths of the seventh and eighth current paths in series so that the linear current paths have a same current direction, fourth current paths which include a plurality of linear current paths lying in parallel to the current path direction of the first current paths on a second plane which confronts the first plane in parallel by being spaced out therefrom, fifth current paths which include a plurality of linear current paths lying in parallel to each other, and lie on the second plane to have a parallel mirror-image relation with the fourth current paths, sixth current paths which lie round beside the fourth and fifth current paths along the second plane to connect all linear current paths of the fourth and fifth current paths in series so that the linear current paths have the same current direction, tenth current paths which include a plurality of linear current paths lying in parallel to each other along the direction perpendicular to the current path direction of the fourth current paths on a fourth plane which confronts the second plane in parallel and in close vicinity thereto, eleventh current paths which include a plurality of linear current paths lying in parallel to each other, and lie on the fourth plane to have a parallel mirror-image relation with the tenth current paths, and twelfth current paths which lie round beside the tenth and eleventh current paths along the fourth plane to connect all linear current paths of the tenth and eleventh current paths in series so that the linear current paths have the same current direction, and having the disable circuits lying on the third, sixth, ninth and twelfth current paths.
The invention at this viewpoint is designed to dispose the disable circuits on the third, sixth, ninth and twelfth paths, i.e., the roundabout current paths, of the coil loop, and consequently a magnetic field created by the d.c. bias current does not affect the static magnetic field of the imaging space.
(7) The invention at other viewpoint intending to solve the above-mentioned problem resides in an RF coil of any one of the items (1) through (6), which is characterized in that the RF choke circuit comprises an inductor.
The invention at this viewpoint is designed to use an inductor as an RF choke circuit, and consequently a signal transmission path having large impedance values in the RF domain and small resistance values in the d.c. domain can be accomplished.
(8) The invention at other viewpoint intending to solve the above-mentioned problem resides in an RF coil of any one of the items (1) through (6), which is characterized in that the RF choke circuit comprises a parallel circuit of an inductor and a capacitor.
The invention at this viewpoint is designed to use a parallel circuit of an inductor and a capacitor as an RF choke circuit, and consequently a signal transmission path having large impedance values in the RF domain and small resistance values in the d.c. domain can be accomplished.
(9) The invention at other viewpoint intending to solve the above-mentioned problem resides in an RF coil of any one of the items (1) through (6), which is characterized in that the RF choke circuit comprises a serial circuit of an inductor and a diode.
The invention at this viewpoint is designed to use a serial circuit of an inductor and a diode as an RF choke circuit, and consequently a signal transmission path having large impedance values in the RF domain and small resistance values in the d.c. domain can be accomplished.
(10) The invention at other viewpoint intending to solve the above-mentioned problem resides in a magnetic resonance imaging apparatus for forming an image based on a magnetic resonance signal which is acquired by use of a static magnetic field, gradient magnetic field and RF magnetic field, and is characterized by including an RF coil which generates the RF magnetic field and has disable circuits each of which is a parallel connection of a capacitor and a serial circuit of an inductor and a diode and is connected in series to the coil loop, and further has RF choke circuits which form a d.c. bias feed path for the diodes by connecting points of equal RF potential on the coil loop.
The invention at this viewpoint is designed to provide the RF coil for generating the RF magnetic field with a bias feed path of the disable circuit based on the connection of points of equal RF potential on the coil loop through RF choke circuits. Accordingly, the d.c. bias current flows through the RF choke circuits instead of the main loop of the RF coil, while the RF signal goes through the main loop instead of the RF choke circuits, and consequently it is possible to feed the d.c. bias current and RF signal at the same point.
(11) The invention at other viewpoint intending to solve the above-mentioned problem resides in a magnetic resonance imaging apparatus of the item (10), which is characterized in that the RF coil includes a plurality of linear main current paths lying in parallel to each other on a plane, and roundabout current paths which lie round beside the main current paths on the plane to connect the main current paths in series so that the main current paths have a same current direction, and has the disable circuits lying on the roundabout current paths.
The invention at this viewpoint is designed to dispose the disable circuits on the roundabout current paths of the coil loop, and consequently a magnetic field created by the d.c. bias current does not affect the static magnetic field of the imaging space.
(12) The invention at other viewpoint intending to solve the above-mentioned problem resides in a magnetic resonance imaging apparatus of the item (10), which is characterized in that the RF coil includes a first current paths which include a plurality of linear current paths lying in parallel to each other on a plane, second current paths which include a plurality of linear current paths lying in parallel to each other, and lie on the plane to have a parallel mirror-image relation with the first current paths, and third current paths which lie round beside the first and second current paths along the plane to connect all linear current paths of the first and second current paths in series so that the linear current paths have a same current direction, and has the disable circuits lying on the third current paths.
The invention at this viewpoint is designed to dispose the disable circuits on the third current paths, i.e., the roundabout current paths, of the coil loop, and consequently a magnetic field created by the d.c. bias current does not affect the static magnetic field of the imaging space.
(13) The invention at other viewpoint intending to solve the above-mentioned problem resides in a magnetic resonance imaging apparatus of the item (10), which is characterized in that the RF coil includes a first current paths which include a plurality of linear current paths lying in parallel to each other on a first plane, second current paths which include a plurality of linear current paths lying in parallel to each other, and lie on the first plane to have a parallel mirror-image relation with the first current paths, third current paths which lie round beside the first and second current paths along the first plane to connect all linear current paths of the first and second current paths in series so that the linear current paths have a same current direction, fourth current paths which include a plurality of linear current paths lying in parallel to the current path direction of the first current paths on a second plane which confronts the first plane in parallel by being spaced out therefrom, fifth current paths which include a plurality of linear current paths lying in parallel to each other, and lie on the second plane to have a parallel mirror-image relation with the fourth current paths, and sixth current paths which lie round beside the fourth and fifth current paths along the second plane to connect all linear current paths of the fourth and fifth current paths in series so that the linear current paths have the same current direction, and has the disable circuits lying on the third and sixth current paths.
The invention at this viewpoint is designed to dispose the disable circuits on the third and sixth current paths, i.e., the roundabout current paths, of the coil loop, and consequently a magnetic field created by the d.c. bias current does not affect the static magnetic field of the imaging space.
(14) The invention at other viewpoint intending to solve the above-mentioned problem resides in a magnetic resonance imaging apparatus of the item (10), which is characterized in that the RF coil includes a first current paths which include a plurality of linear current paths lying in parallel to each other on a first plane, second current paths which include a plurality of linear current paths lying in parallel to each other, and lie on the first plane to have a parallel mirror-image relation with the first current paths, third current paths which lie round beside the first and second current paths along the first plane to connect all linear current paths of the first and second current paths in series so that the linear current paths have a same current direction, seventh current paths which include a plurality of linear current paths lying in parallel to each other along the direction perpendicular to the current path direction of the first current paths on a third plane which confronts the first plane in parallel and in close vicinity thereto, eighth current paths which include a plurality of linear current paths lying in parallel to each other, and lie on the third plane to have a parallel mirror-image relation with the seventh current paths, and ninth current paths which lie round beside the seventh and eighth current paths along the third plane to connect all linear current paths of the seventh and eighth current paths in series so that the linear current paths have a same current direction, and has the disable circuits lying on the third and ninth current paths.
The invention at this viewpoint is designed to dispose the disable circuits on the third and ninth current paths, i.e., the roundabout current paths, of the coil loop, and consequently a magnetic field created by the d.c. bias current does not affect the static magnetic field of the imaging space.
(15) The invention at other viewpoint intending to solve the above-mentioned problem resides in a magnetic resonance imaging apparatus of the item (10), which is characterized in that the RF coil includes a first current paths which include a plurality of linear current paths lying in parallel to each other on a first plane, second current paths which include a plurality of linear current paths lying in parallel to each other, and lie on the first plane to have a parallel mirror-image relation with the first current paths, third current paths which lie round beside the first and second current paths along the first plane to connect all linear current paths of the first and second current paths in series so that the linear current paths have a same current direction, seventh current paths which include a plurality of linear current paths lying in parallel to each other along the direction perpendicular to the current path direction of the first current paths on a third plane which confronts the first plane in parallel and in close vicinity thereto, eighth current paths which include a plurality of linear current paths lying in parallel to each other, and lie on the third plane to have a parallel mirror-image relation with the seventh current paths, ninth current paths which lie round beside the seventh and eighth current paths along the third plane to connect all linear current paths of the seventh and eighth current paths in series so that the linear current paths have a same current direction, fourth current paths which include a plurality of linear current paths lying in parallel to the current path direction of the first current paths on a second plane which confronts the first plane in parallel by being spaced out therefrom, fifth current paths which include a plurality of linear current paths lying in parallel to each other, and lie on the second plane to have a parallel mirror-image relation with the fourth current paths, sixth current paths which lie round beside the fourth and fifth current paths along the second plane to connect all linear current paths of the fourth and fifth current paths in series so that the linear current paths have the same current direction, tenth current paths which include a plurality of linear current paths lying in parallel to each other along the direction perpendicular to the current path direction of the fourth current paths on a fourth plane which confronts the second plane in parallel and in close vicinity thereto, eleventh current paths which include a plurality of linear current paths lying in parallel to each other, and lie on the fourth plane to have a parallel mirror-image relation with the tenth current paths, and twelfth current paths which lie round beside the tenth and eleventh current paths along the fourth plane to connect all linear current paths of the tenth and eleventh current paths in series so that the linear current paths have the same current direction, and has the disable circuits lying on the third, sixth, ninth and twelfth current paths.
The invention at this viewpoint is designed to dispose the disable circuits on the third, sixth, ninth and twelfth current paths, i.e., the roundabout current paths, of the coil loop, and consequently a magnetic field created by the d.c. bias current does not affect the static magnetic field of the imaging space.
(16) The invention at other viewpoint intending to solve the above-mentioned problem resides in a magnetic resonance imaging apparatus of any one of the items (10) through (15), which is characterized in that the RF choke circuit comprises an inductor.
The invention at this viewpoint is designed to use an inductor as an RF choke circuit, and consequently a signal transmission path having large impedance values in the RF domain and small resistance values in the d.c. domain can be accomplished.
(17) The invention at other viewpoint intending to solve the above-mentioned problem resides in a magnetic resonance imaging apparatus of any one of the items (10) through (15), which is characterized in that the RF choke circuit comprises a parallel circuit of an inductor and a capacitor.
The invention at this viewpoint is designed to use a parallel circuit of an inductor and a capacitor as an RF choke circuit, and consequently a signal transmission path having large impedance values in the RF domain and small resistance values in the d.c. domain can be accomplished.
(18) The invention at other viewpoint intending to solve the above-mentioned problem resides in a magnetic resonance imaging apparatus of any one of the items (10) through (15), which is characterized in that the RF choke circuit comprises a serial circuit of an inductor and a diode.
The invention at this viewpoint is designed to use a serial circuit of an inductor and a diode as an RF choke circuit, and consequently a signal transmission path having large impedance values in the RF domain and small resistance values in the d.c. domain can be accomplished.
Therefore, the present invention can accomplish RF coils which prevent the bias current of the disable circuits from adversely affecting the static magnetic field, and magnetic resonance imaging apparatus having the RF coils.
Further objects and advantages of the present invention will be apparent from the following description of the preferred embodiments of the invention as illustrated in the accompanying drawings.